Complete gene sequence diversity, amplification, and natural selection of the Plasmodium vivax Duffy binding protein...

The Duffy binding ligand domain of Plasmodium vivax (PvDBPII) interacts with Duffy blood-group antigen on the surface of reticulocytes during host cell invasion process. Although diversity of this domain has been analysed among worldwide isolates, the evolution of the complete PvDBP gene remains to be explored.

In total, 232 P. vivax isolates from northwestern, northeastern, eastern, and southern Thailand were included for analyses of the complete gene sequence, copy number variation and duplication genotypes of Pvdbp. The Duffy blood-group genotypes of the patient were also determined.

Pvdbp duplication, all of the Cambodian type, was detected in 22 isolates (9.48%), characterized by identical copies (n = 17) and microheterogeneity between copies (n = 5). Across 254 sequences including duplicated copies, nucleotide diversity was highest in PvdbpII. Positive selection, evidenced by excess nonsynonymous over synonymous substitutions, occurred in both the 5' region and PvdbpII. Codon-based analysis revealed 26 positively selected codons distributed across the protein; 22 of these overlapped predicted B cell and/or T cell epitopes. Insertions and deletions including frameshift mutations were found outside PvdbpII apart from an indel in this domain, while recombination breakpoints were confined to PvdbpII and the 3' region. Parasite isolates from each endemic region displayed population structure. No significant difference in Duffy phenotype frequencies was found between malaria patients in this study and healthy blood donors from reported data.

While PvdbpII remains the most variable domain, sequence diversity occurred outside this domain. Cambodian-type Pvdbp duplications, often with identical sequences, may enhance immune evasion via increased gene dosage. Positive selection is broadly distributed and likely driven by host immune pressure. Whether positive selection outside PvdbpII is relevant for vaccine design requires further investigation.